CN111912709B - Method for accurately measuring compressive strength of concrete material under variable confining pressure state - Google Patents
Method for accurately measuring compressive strength of concrete material under variable confining pressure state Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
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- G06F—ELECTRIC DIGITAL DATA PROCESSING
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0001—Type of application of the stress
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
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Abstract
The invention discloses a method for accurately measuring the compressive strength of concrete materials under a variable confining pressure state, which comprises the steps of establishing a function expression between an internal pressure range, a loading range and each direction strain at each position through a finite element model on the one hand; further, a mathematical expression convenient for practical application is obtained by correlating the thickness, strain value and axial strength of a test piece tested by the experimental device with the relationship between the strain and the internal pressure in different loading ranges in finite element analysis, and the compressive strength of the concrete material under the variable confining pressure state can be obtained by calculating according to any one of actually obtained values of offset stress, volume strain, passive confining pressure and the like through the mathematical expression. The invention relates finite element model analysis and specific parameter measurement experiments, thereby establishing a constitutive equation of the material under a complex stress state, namely the relationship between the compressive strength, the partial stress, the volume strain and the like and the passive confining pressure, further measuring the compressive strength of the concrete material under a variable confining pressure state, and having the advantages of accuracy, convenience and the like.
Description
Technical Field
The invention belongs to the technical field of concrete brittle material strength testing, and particularly relates to a method for accurately measuring the compressive strength of a concrete brittle material under a variable confining pressure state.
Background
The concrete material is widely applied to major protection projects such as weapon storehouses, nuclear engineering containment vessels and the like, and has important significance for the research of the compressive strength of the concrete material. The concrete material is a hydrostatic pressure related material, the compressive strength of the concrete material is closely dependent on the change of hydrostatic pressure in the bearing process, and the understanding and understanding of the mechanism of the hydrostatic pressure influencing the compressive strength are the prerequisites for reasonably designing and applying the material. Confining pressure experiments for such materials are generally classified into two main categories, active and passive confining pressure. Typical active confining pressure experiments are usually completed by means of a triaxial experimental instrument, the constitution of the active confining pressure experiments is complex and expensive, and the active confining pressure experiments only provide constant confining pressure with small amplitude (within 100 MPa), cannot flexibly match different axial pressure loading conditions, and cannot adapt to the experiment requirements under the state of high confining pressure (hundreds of MPa). The typical passive confining pressure is usually realized by sleeving a high-strength rigid ring outside a test piece, and the rigid ring is generally considered not to be subjected to plastic deformation in the experimental process, so that the passive confining pressure with extremely large amplitude can be provided. At present, the confining pressure experiment basically measures a point value, namely the compressive strength when a certain confining pressure value (such as the maximum value) is measured, and the variable confining pressure condition determination cannot be realized; the simplified analysis is carried out on the test piece according to the quasi-one-dimensional strain state, the change condition of the confining pressure value in the loading process of the test piece is not paid enough attention, and therefore sufficient information cannot be provided in the aspect of establishing the constitutive equation of the material under the complex stress state.
Disclosure of Invention
Based on the technical problem, the invention provides a method for accurately measuring the compressive strength of a concrete material in a variable confining pressure state.
The technical solution adopted by the invention is as follows:
a method for accurately measuring the compressive strength of a concrete material under a variable confining pressure state adopts a device capable of establishing the relationship among displacement, strain and compressive strength of a cylindrical concrete material test piece under vertical loading, the device comprises a high-strength steel ring, a cylindrical concrete material test piece, a high-strength steel cylinder auxiliary loading end plate, a strain gauge, a displacement sensor and a testing machine, the cylindrical concrete material test piece is placed in the high-strength steel ring, the high-strength steel cylinder auxiliary loading end plate is tightly attached to two ends of the cylindrical concrete material test piece, and then the high-strength steel cylinder auxiliary loading end plate is integrally arranged between the loading end plates of the testing machine;
the device comprises a high-strength steel ring, a plurality of strain gauges, a plurality of displacement sensors, a load sensor and a computer terminal, wherein the strain gauges are uniformly arranged on the high-strength steel ring along the axial direction and the circumferential direction;
The method comprises the following steps:
s1, preparing 10 pairs of strain gauges, pasting the strain gauges at five positions from top to bottom of front and rear symmetrical parts on the outer side of a high-strength steel ring along the axial direction and the annular direction respectively, and numbering the strain gauges A, B, C, D and E in sequence;
s2, creating a numerical calculation model under the action of internal pressure according to the actual size and material properties of the high-strength steel ring;
s3 in finite element analysis, using transverse central line of high-strength steel ring as symmetry axis, respectively in height range delta E [ h/2, h]Applying uniform internal pressure p every h/10 within the range, and outputting strain epsilon of unit corresponding to the position of the strain gauge in step S1 i A I ═ A, …, E and ε i H I ═ a, …, E; wherein, the superscripts A and H represent axial direction and annular direction respectively;
s4 analyzes the relation between the input internal pressure p and the height range delta and the output strain in the step S3 by a numerical method,
obtaining a function expression between the internal pressure p, the height range and each position of each strain through regression analysis,
s5, uniformly smearing lubricating oil on the surfaces of the cylindrical concrete material test piece and the high-strength steel cylinder auxiliary loading end plate and on the inner surface of the high-strength steel ring; placing a cylindrical concrete material test piece into a high-strength steel circular ring, and respectively installing high-strength steel cylindrical auxiliary loading end plates at the upper side and the lower side;
S6, placing the whole body combined in the step S5 between loading end plates of a testing machine, and uniformly arranging displacement sensors between the loading end plates of the testing machine in the circumferential direction;
s7, respectively connecting the strain gauge, the displacement sensor and the load sensor carried by the testing machine with a computer terminal;
s8, the testing machine is controlled by the computer terminal to load, and the time history curves F (t) of the load sensor, the strain gauge and the displacement sensor are recorded in real time, wherein epsilon i j (t),dis(t)；
S9, processing the data recorded in the step S8 in real time: for a given time t, calculating the axial strength of the test piece according to the load sensor signal,
σ z (t)＝F(t)/A(t) (3-1)
in the formula: sigma z (t) axial strength of the cylindrical concrete material test piece, A (t) cross section area of the test piece at the time t, d diameter of the test piece,
the ring direction strain value is measured by a strain gauge at the position C of the high-strength steel ring at the moment t;
calculating the thickness of the specimen by means of the displacement sensor data dis (t), and calculating the axial strain on the basis thereof,
T(t)＝h-dis(t) (4-1)
ε axial (t)＝dis(t)/h (4-2)
get
Wherein epsilon axial (t)，ε hoop (t)，ε radial (t) respectively representing the axial strain value, the circumferential strain value and the radial strain value of the test piece at the moment t;
s10 is determined by correlating T (t),
Obtaining the radial stress born by the test piece at the moment according to the relation between the internal pressure and the loading range amplitude and the strain value obtained in the step S4 
In theory, the following formula should hold true,
because of the existence of test errors, the values of the radial stress derived from the strain gauges at different positions in the test process are different, and in the actual test, the values can be obtained
The average value of the measured values is used as the radial stress value born by the test piece at the moment,
s11 is determined by axial stress sigma z (t) and radial stress σ R (t) calculating the passive confining pressure p (t) and the offset stress sigma of the test piece dev (t) and volume strain ε volum (t)，
σ dev (t)＝|σ z (t)-σ R (t)| (7-2)
ε volum (t)＝(1+ε axial (t))(1+ε radial (t)) 2 -1 (7-3)
Wherein epsilon axial (t)，ε radial (t) respectively representing the axial strain value and the radial strain value of the test piece at the moment t;
s12 relating the formulas in step S9 and step S11 to determine the axial compression strength sigma of the test piece z (t) bias stress σ dev (t) relationship to passive confining pressure p (t); and passive confining pressure p (t) and volume strain epsilon volum (t) the relationship between (a) and (b),
σ z (t)＝f(p(t)) (8-1)
σ dev (t)＝f(p(t)) (8-2)
p(t)＝f(ε volum (t)) (8-3)
s13 repeating steps S5-S12, using the average values to establish the passive confining pressure p (t) and the axial compression strength sigma z (t) bias stress σ dev (t) volume strain ε volum (t) the relationship between (a) and (b),
s14 performs parameter regression through a numerical method to obtain a mathematical expression convenient for practical use, in the form of,
σ z ＝k 1 p+c 1 (10-1)
σ dev ＝k 2 p+c 2 (10-2)
p＝k 3 ε volum +c 3 (10-3)
in the formula, σ z 、σ dev 、ε volum And p is axial compressive strength, partial stress, volume strain and passive confining pressure respectively; parameter k 1 ,k 2 ,k 3 ，c 1 ,c 2 ,c 3 Depending on the material composition of the cylindrical concrete material test piece;
according to the formula, the relationship between the axial compressive strength, the offset stress and the volume strain in the variable confining pressure state and the passive confining pressure can be established, so that the compressive strength of the concrete material in the variable confining pressure state can be accurately measured.
The height H of the high-strength steel ring meets the condition that: h +2H is greater than H, wherein H is the height of the cylindrical concrete material test piece; h is the height of the high-strength steel cylinder auxiliary loading end plate.
The diameter of the auxiliary loading end plate of the cylindrical concrete material test piece and the high-strength steel cylinder is D, the inner diameter of the high-strength steel ring is D, and D is slightly larger than D, so that lubricating oil can be conveniently smeared on the surface of the auxiliary loading end plate of the cylindrical concrete material test piece and the high-strength steel cylinder and on the inner surface of the high-strength steel ring, and friction between contact surfaces is reduced.
The beneficial technical effects of the invention are as follows:
the invention relates finite element model analysis and specific parameter measurement experiments, thereby establishing a constitutive equation of the material under a complex stress state, namely the relationship between the compressive strength, the partial stress, the volume strain and the like and the passive confining pressure, further accurately and conveniently measuring the compressive strength and the like of the concrete material under a variable confining pressure state, and having practical value for application research and the like of the concrete material.
Drawings
The invention will be further described with reference to the following detailed description and drawings:
FIG. 1 is a flow chart of a method for accurately measuring the compressive strength of a concrete material under a variable confining pressure state according to an embodiment of the invention;
FIG. 2 is a component assembly diagram of a test device according to an embodiment of the present invention; wherein: (1) a high strength steel ring; (2) a cylindrical concrete material test piece; (3) the high-strength steel cylinder auxiliary loading end plate (4) and lubricating oil; (5) and a strain gauge; (6) a displacement sensor;
FIG. 3 is a schematic diagram illustrating a bonding position of a strain gauge on an outer surface of a high-strength steel ring according to an embodiment of the present invention;
FIG. 4 is a diagram of a finite element analysis model in an embodiment of the present invention (the darkened areas are the elements that output axial and hoop strain);
FIG. 5 is an assembled view of test parts according to an embodiment of the present invention; wherein: (1) the main view structure principle schematic diagram of the whole body after assembly, (2) is a 1-1 section view, and (3) is a 2-2 section view;
FIG. 6 is a schematic view of the overall structure of the testing apparatus according to the embodiment of the present invention;
FIG. 7 is a diagram of the relationship between the axial and hoop strains and confining pressure of the unit at different positions on the outer surface of the model in the range of taking the middle of the ring as the axis of symmetry h in the finite element analysis according to the embodiment of the present invention;
FIG. 8 is a graph of the relationship between the axial and hoop strains and confining pressure of the elements at different positions on the outer surface of the model in the range of the ring middle as the symmetry axis h/2 in the finite element analysis according to the embodiment of the present invention;
FIG. 9 is a cloud chart of the strain distribution of the steel ring under the action of pressure applied to the test piece in the full height range according to the embodiment of the invention;
FIG. 10 is a graph showing the relationship between the axial stress, the confining pressure stress and the axial strain of a concrete material according to an embodiment of the present invention;
FIG. 11 is a graph showing the relationship between the measured confining pressure stress and the volume strain of a concrete material according to an embodiment of the present invention;
FIG. 12 is a graph showing the relationship between the measured concrete material offset stress and the confining pressure stress according to the embodiment of the present invention.
In fig. 5-6: 1. a high strength steel ring; 2. a cylindrical concrete material test piece; 3. the high-strength steel cylinder assists the loading end plate; 4. lubricating oil; 5. a strain gauge; 6. a displacement sensor; 7. a signal line; 8. loading an end plate of the testing machine; 9. a dynamic acquisition instrument; 10. and (4) a computer terminal.
Detailed Description
The invention provides a method for accurately measuring the compressive strength of a concrete material under a variable confining pressure state, which is an accurate measurement method for the compressive strength of the concrete material under the variable confining pressure state based on numerical simulation, test, data acquisition and processing. The method combines numerical simulation, test, data acquisition and processing, and can realize accurate and convenient determination of the compressive strength of the concrete material under the variable confining pressure state.
The method of the invention needs to use a device for establishing the relationship among the displacement, the strain and the compressive strength of the cylindrical test piece under the vertical loading, as shown in figures 2-3 and 5-6, the device comprises: the device comprises a high-strength steel ring 1, a cylindrical concrete material test piece 2, a high-strength steel cylinder auxiliary loading end plate 3, lubricating oil 4, a strain gauge 5, a displacement sensor 6 and the like. Lubricating oil is paintd on each surface of cylindrical concrete class material test piece and the supplementary loading end plate of high strength steel cylinder, high strength steel ring internal surface, put into steel ring inboard and arrange jointly between testing machine loading end plate 8 after the supplementary loading end plate upper and lower parcel test piece, the foil gage sets up 10 pairs altogether, evenly arranges in 5 positions departments of top-down of ring bisymmetry surface along axial and hoop, records the axial strain and the hoop strain of ring in loading process. The displacement sensor is evenly arranged between the upper loading end plate and the lower loading end plate of the testing machine along the annular direction, the testing machine is controlled by the computer terminal to be loaded, the time history curves of the load sensor, the strain gauge and the displacement sensor are recorded in real time, and the recorded data of the load sensor, the strain gauge and the displacement sensor are processed in real time through the computer.
The height (H) of the high-strength steel circular ring is H +2H larger than H (H: the height of the cylindrical concrete material test piece; H: the height of the high-strength steel cylinder auxiliary loading end plate).
The diameter (D) of the cylindrical concrete material test piece and the high-strength steel cylinder auxiliary loading end plate is slightly smaller than the inner diameter (D) of the high-strength steel ring, so that lubricating oil can be conveniently smeared on each contact surface, friction between the contact surfaces is reduced, and the accuracy of test data is improved.
The displacement sensor is arranged between the upper end plate and the lower end plate of the testing machine along the annular direction, and is connected with the computer terminal 10 through a flexible signal line 7.
The invention discloses a method for accurately measuring the compressive strength of a concrete material under a variable confining pressure state, which is a method based on numerical simulation, test testing, data acquisition and processing. On one hand, the method for measuring the relationship between the internal pressure and the loading range and the strain in each position is established through a finite element model, and comprises the following steps: establishing a finite element model of a high-strength steel ring, respectively applying uniform internal pressure every h/10 within the range of h/2 to h by taking the middle part of the ring as a symmetry axis, outputting the axial and circumferential strain of a unit at the position same as a strain gauge of an experimental device, analyzing the relation between the amplitude and height of the input internal pressure and the output strain by a numerical method, and establishing a function expression between the internal pressure and loading range and each strain at each position.
Further, by correlating the thickness, the strain value, the axial strength of a test piece tested by the experimental device and the relation between the strain and the confining pressure in different loading ranges in finite element analysis, a passive confining pressure value, a partial stress, a volume strain and a compressive strength borne by the test piece at the time t are obtained, the relation between the compressive strength, the partial stress, the volume strain and the passive confining pressure of the test piece is determined, the above processes are repeated for multiple times, and the average value is taken to establish the relation between the passive confining pressure and the axial strength, the partial stress and the volume strain; parameter regression is carried out on the concrete material through a numerical method to obtain a mathematical expression which is convenient for practical application, and the compressive strength of the concrete material under the variable confining pressure state can be obtained through calculation according to any numerical value of actually obtained partial stress, volume strain, passive confining pressure and the like through the mathematical expression.
As shown in fig. 1, a method for accurately measuring the compressive strength of a concrete material under a variable confining pressure state specifically comprises the following steps:
s1 cylindrical concrete material test pieces, a high-strength steel ring and two high-strength steel cylinders are prepared to assist loading end plates, 10 pairs of strain gauges are prepared simultaneously, the strain gauges are pasted on the front and rear symmetrical parts of the outer side of the high-strength steel ring from top to bottom along the axial direction and the circumferential direction respectively, and the serial numbers of the strain gauges are A, B, C, D and E.
S2, according to the actual size and material properties of the high-strength steel circular ring, a numerical calculation model under the action of internal pressure is created.
S3 in finite element analysis, using transverse central line of high-strength steel ring as symmetry axis, respectively in height range delta E [ h/2, h]Applying uniform internal pressure p every h/10 within the range, and outputting corresponding stepsStrain epsilon of the cell at the location of the strain gauge in step S1 i A I ═ A, …, E and ε i H I ═ a, …, E; wherein the superscripts a, H represent the axial and circumferential directions, respectively.
And applying uniform internal pressure p every h/10 within the height range delta epsilon [ h/2, h ], namely, gradually compressing the cylindrical concrete material test piece in the experimental process from the height h to the height h/2, and setting the compression amplitude as h/10.
S4 analyzes the relation between the input internal pressure amplitude p and the height range delta and the output strain in the step S3 through a numerical method,
obtaining a function expression among the internal pressure p, the height range (loading range) and the each-directional strain at each position through regression analysis,
s5, uniformly smearing lubricating oil on the surfaces of the cylindrical concrete material test piece and the high-strength steel cylinder auxiliary loading end plate and on the inner surface of the high-strength steel ring; a cylindrical concrete material test piece is placed inside a high-strength steel circular ring, and high-strength steel cylindrical auxiliary loading end plates are respectively arranged on the upper side and the lower side of the cylindrical concrete material test piece.
S6, the whole combined in the step S5 is placed between loading end plates of the testing machine, and displacement sensors are uniformly arranged between the loading end plates in the circumferential direction.
And S7, connecting the strain gauge, the displacement sensor and the load sensor carried by the testing machine with the computer terminal through the dynamic acquisition instrument respectively.
S8, loading the test machine through the control of a computer terminal, recording the time history curves F (t) of the load sensor, the strain gauge and the displacement sensor in real time,
dis(t)。
the S9 calculation program processes the data recorded in the step S8 in real time: for a given time t, calculating the axial strength of the test piece according to the load sensor signal,
σ z (t)＝F(t)/A(t) (3-1)
in the formula: sigma z (t) axial strength of the cylindrical concrete material test piece, A (t) cross section area of the test piece at the time t, d diameter of the test piece,
and (4) measuring the ring direction strain value of the strain gauge at the position C of the high-strength steel ring at the time t.
Calculating the thickness of the specimen by means of the displacement sensor data dis (t), and calculating the axial strain on the basis thereof,
T(t)＝h-dis(t) (4-1)
ε axial (t)＝dis(t)/h (4-2)
get
Wherein epsilon axial (t)，ε hoop (t)，ε radial And (t) respectively representing the axial strain value, the circumferential strain value and the radial strain value of the test piece at the moment t.
S10 is determined by correlating T (t),
Obtaining the radial stress born by the test piece at the moment according to the relation between the internal pressure and the loading range amplitude and the strain value obtained in the step S4 
Theoretically, the following formula shouldIt is true that the first and second sensors,
because of the existence of test errors, the values of the radial stress derived from the strain gauges at different positions in the test process are different, and in the actual test, the values can be obtained
The average value of the radial stress values of the test piece at the moment is taken as the radial stress value born by the test piece,
s11 is formed by axial stress sigma z (t) and radial stress σ R (t) calculating the passive confining pressure p (t) and the offset stress sigma of the test piece dev (t) and volume strain ε volum (t)，
σ dev (t)＝|σ z (t)-σ R (t)| (7-2)
ε volum (t)＝(1+ε axial (t))(1+ε radial (t)) 2 -1 (7-3)
Wherein epsilon axial (t)，ε radial And (t) respectively representing the axial strain value of the test piece at the moment t and the radial strain value of the high-strength steel ring at the moment t.
S12 relating the formulas in step S9 and step S11 to determine the axial compression strength sigma of the test piece z (t) bias stress σ dev (t) relationship to passive confining pressure p (t); and passive confining pressure p (t) and volume strain epsilon volum (t) the relationship between (a) and (b),
σ z (t)＝f(p(t)) (8-1)
σ dev (t)＝f(p(t)) (8-2)
p(t)＝f(ε volum (t)) (8-3)
s13 repeating the steps S5-S12, and applying the average values to establish the passive confining pressure p (t) and the axial compression strength sigma z (t) stress offset (offset stress) σ dev (t) volume strain ε volum (t) the relationship between (a) and (b),
s14 performs parameter regression through a numerical method to obtain a mathematical expression convenient for practical use, in the form of,
σ z ＝k 1 p+c 1 (10-1)
σ dev ＝k 2 p+c 2 (10-2)
p＝k 3 ε volum +c 3 (10-3)
in the formula, σ z 、σ dev 、ε volum And p is axial compressive strength, partial stress, volume strain and passive confining pressure respectively; parameter k 1 ,k 2 ,k 3 ，c 1 ,c 2 ,c 3 Is constant and depends on the material composition of the cylindrical concrete material test piece. That is, different cylindrical concrete material test pieces correspond to the parameter k 1 ,k 2 ,k 3 ，c 1 ,c 2 ,c 3 The above parameters can be determined by the above method steps, however.
According to the formula, the relationship between the axial compressive strength, the offset stress and the volume strain in the variable confining pressure state and the passive confining pressure can be established, so that the compressive strength of the concrete material in the variable confining pressure state can be accurately measured. Namely, the compressive strength of the concrete material under the variable confining pressure state can be calculated according to any one of actually obtained values of partial stress, volume strain, passive confining pressure and the like through the mathematical expression.
Parts not described in the above embodiments can be realized by taking or referring to the prior art.
It is to be understood that the above description is not intended to limit the present invention, and the present invention is not limited to the above embodiments, and those skilled in the art may make modifications, alterations, additions or substitutions within the spirit and scope of the present invention.
Claims (3)
1. A method for accurately measuring the compressive strength of a concrete material under a variable confining pressure state is characterized in that a device capable of establishing the relationship among displacement, strain and compressive strength of a cylindrical concrete material test piece under vertical loading is adopted, the device comprises a high-strength steel ring, a cylindrical concrete material test piece, a high-strength steel cylinder auxiliary loading end plate, a strain gauge, a displacement sensor and a testing machine, the cylindrical concrete material test piece is placed in the high-strength steel ring, the high-strength steel cylinder auxiliary loading end plate abuts against two ends of the cylindrical concrete material test piece, and then the high-strength steel cylinder auxiliary loading end plate is integrally arranged between the loading end plates of the testing machine;
The device comprises a high-strength steel ring, a plurality of strain gauges, a plurality of displacement sensors, a load sensor and a computer terminal, wherein the strain gauges are uniformly arranged on the high-strength steel ring along the axial direction and the circumferential direction;
the method comprises the following steps:
s1, preparing 10 pairs of strain gauges, pasting the strain gauges at five positions from top to bottom of front and rear symmetrical parts on the outer side of a high-strength steel ring along the axial direction and the annular direction respectively, and numbering the strain gauges A, B, C, D and E in sequence;
s2, creating a numerical calculation model under the action of internal pressure according to the actual size and material properties of the high-strength steel ring;
s3 in finite element analysis, using transverse central line of high-strength steel ring as symmetry axis, respectively in height range delta E [ h/2, h]Applying uniform internal pressure p every h/10 within the range, and outputting strain of the unit at the position corresponding to the strain gauge in step S1
And
wherein, the superscripts A and H represent axial direction and annular direction respectively;
s4 analyzes the relation between the input internal pressure p and the height range delta and the output strain in the step S3 by a numerical method,
obtaining a function expression between the internal pressure p, the height range and each position of each strain through regression analysis,
S5, uniformly smearing lubricating oil on the surfaces of the cylindrical concrete material test piece and the high-strength steel cylinder auxiliary loading end plate and on the inner surface of the high-strength steel ring; placing a cylindrical concrete material test piece into a high-strength steel circular ring, and respectively installing high-strength steel cylindrical auxiliary loading end plates at the upper side and the lower side;
s6, placing the whole combined in the step S5 between loading end plates of a testing machine, and uniformly arranging displacement sensors between the loading end plates of the testing machine along the circumferential direction;
s7, connecting the strain gauge, the displacement sensor and the load sensor of the tester with the computer terminal respectively;
s8 loading the test machine by controlling the test machine through a computer terminal and recording the load in real timeSensor, strain gauge and displacement sensor time history curve
S9, processing the data recorded in the step S8 in real time: for a given time t, calculating the axial strength of the test piece according to the load sensor signal,
σ z (t)＝F(t)/A(t) (3-1)
in the formula: sigma z (t) axial strength of the cylindrical concrete material test piece, A (t) cross section area of the test piece at the time t, d diameter of the test piece,
the ring direction strain value is measured by a strain gauge at the position C of the high-strength steel ring at the moment t;
calculating the thickness of the specimen by means of the displacement sensor data dis (t), and calculating the axial strain on the basis thereof,
T(t)＝h-dis(t) (4-1)
ε axial (t)＝dis(t)/h (4-2)
Get the
Wherein epsilon axial (t)，ε hoop (t)，ε radial (t) respectively obtaining an axial strain value, a circumferential strain value and a radial strain value of the test piece at the moment t;
s10 is determined by correlating T (t),
Correlation of the internal pressure, the magnitude of the load range and the strain value obtained in step S4Obtaining the radial stress of the test piece at that moment
In theory, the following equation should hold,
because of the existence of test errors, the values of the radial stress derived from the strain gauges at different positions in the test process are different, and in the actual test, the values can be obtained
The average value of the radial stress values of the test piece at the moment is taken as the radial stress value born by the test piece,
s11 is formed by axial stress sigma z (t) and radial stress σ R (t) calculating the passive confining pressure p (t) and the offset stress sigma of the test piece dev (t) and volume strain ε volum (t)，
σ dev (t)＝|σ z (t)-σ R (t)| (7-2)
ε volum (t)＝(1+ε axial (t))(1+ε radial (t)) 2 -1 (7-3)
Wherein epsilon axial (t)，ε radial (t) respectively representing the axial strain value and the radial strain value of the test piece at the moment t;
s12 relating the formulas in step S9 and step S11 to determine the axial compression strength sigma of the test piece z (t) bias stress σ dev Between (t) and the passive confining pressure p (t)The relationship of (1); and passive confining pressure p (t) and volume strain epsilon volum (t) the relationship between (a) and (b),
σ z (t)＝f(p(t)) (8-1)
σ dev (t)＝f(p(t)) (8-2)
p(t)＝f(ε volum (t)) (8-3)
s13 repeating steps S5-S12, using the average values to establish the passive confining pressure p (t) and the axial compression strength sigma z (t) bias stress σ dev (t) volume strain ε volum (t) the relationship between (a) and (b),
s14 performs parameter regression through a numerical method to obtain a mathematical expression convenient for practical use, in the form of,
σ z ＝k 1 p+c 1 (10-1)
σ dev ＝k 2 p+c 2 (10-2)
p＝k 3 ε volum +c 3 (10-3)
In the formula, σ z 、σ dev 、ε volum And p is axial compressive strength, partial stress, volume strain and passive confining pressure respectively; parameter k 1 ,k 2 ,k 3 ，c 1 ,c 2 ,c 3 Depending on the material composition of the cylindrical concrete material test piece;
according to the formula, the relationship between the axial compressive strength, the offset stress and the volume strain in the variable confining pressure state and the passive confining pressure can be established, so that the compressive strength of the concrete material in the variable confining pressure state can be accurately measured.
2. The method for accurately measuring the compressive strength of the concrete material under the variable confining pressure state as claimed in claim 1, wherein the height H of the high-strength steel ring satisfies the condition that: h +2H is greater than H, wherein H is the height of the cylindrical concrete material test piece; h is the height of the high-strength steel cylinder auxiliary loading end plate.
3. The method for accurately measuring the compressive strength of the concrete material under the variable confining pressure state as claimed in claim 1, wherein: the diameter of cylindrical concrete class material test piece and the supplementary loading end plate of high strength steel cylinder is D, the internal diameter of high strength steel ring is D, and D slightly is greater than D to lubricating oil is evenly paintd at the surface of the supplementary loading end plate of cylindrical concrete class material test piece and high strength steel cylinder to and the high strength steel ring internal surface, reduces the friction between the contact surface.
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